package 实践.class_05;

import java.util.Scanner;

public class Demo_01 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        double side = in.nextDouble();
        System.out.printf("%.2f\n", area(n, side));
        in.close();
    }

    private static double area(int n, double side) {
        return n * side * side / (4 * Math.tan(Math.PI / n));
    }
}
